1. Technical Field
The present invention relates to an image forming apparatus that includes a rotary developing device.
2. Related Art
In an image forming apparatus of full colors for forming an image in accordance with an electronic photograph method, such as a copier, a printer, a multiple function processor or the like, there is an apparatus that includes a rotary developing device which integrally has four developing devices corresponding to respective colors of K (black), C (cyan), M (magenta) and Y (yellow). In the rotary developing device, one developing roll is installed for each developing device.
When the image forming apparatus including the rotary developing device is used to form a full-color image, it is necessary to rotationally drive the rotary developing device and consequently move the respective developing rolls in turn to a development position opposite an image carrier and then switch the development colors. In that case, the positional relationship (angle allocation) where the developing rolls for the respective colors, the toner concentration sensor and the concentration standard member as mentioned above are placed in the rotation direction (around the rotation axis) of the rotary developing device becomes the largest factor in determining the productivity of the image formation. In particular, in a case where on the rotation orbit of the rotary developing device, the angular interval between some of the developing rolls is made wider than the other units, when the rotation of the rotary developing device is stopped so as to move the respective developing rolls in turn to the development position, the stop positions of the placed developing rolls except the development position become discrete. For this reason, unless the positional relationship to the toner concentration sensor and the concentration standard member is properly set, there are fears that the rotation drive control of the rotary developing device is becomes complicated and that the productivity of the image formation is extremely reduced.